future science group 10.4155/BFS.12.6 ISSN 1759-7269 193

The primary objectives of this review are to cover important topics related to biodiesel, which include standards, production, influence of chemical structure on 

fuel properties and traditional feedstocks. Of principal 

interest are the promising alternative oilseed feedstocks 

camelina (Camelina sativa) and field pennycress (Thlaspi 

arvense), which have hitherto attracted considerably less 

attention than algae and jatropha (Jatropha curcas). Also 

discussed are advantages and disadvantages of biodiesel 

relative to conventional petroleum diesel fuel (petrodiesel), energy balance, the influence of free fatty acids 

(FFAs) on production of biodiesel, phase distribution 

during transesterification, optimum reaction conditions, 

the chemical structure of biodiesel and common fatty 

acids (FAs) typically encountered in biodiesel. With an 

emphasis on camelina and field pennycress, the current 

review differentiates itself from numerous predecessors 

by concentrating on alternative nonfood oilseed feedstocks that thrive in temperate climates and, thus, may 

be produced in close proximity to human population 

(and energy consuming) centers.

Definition

Biodiesel is defined by the American Society for Testing 

and Materials (ASTM) as a fuel comprised of monoalkyl 

esters of long-chain FAs derived from vegetable oils or animal fats, designated B100 and meeting the requirements 

of ASTM D6751. The European Standard (EN) 14214 

(European Committee for Standardization) de facto

defines biodiesel as fatty acid methyl esters (FAMEs). 

Consequently, other materials such as neat vegetable oils, 

hydrocarbons prepared therefrom or Fischer–Tropsch 

diesel produced by gasification of biomass do not technically qualify as biodiesel, despite their occasional reference 

as such. As the name implies, biodiesel is intended as a 

bio-based substitute or blend component for middle distillate fuels (petrodiesel) for combustion in compressionignition (diesel) engines, and is therefore not suited for 

spark-ignition (gasoline) engines.

Biodiesel standards

Two of the most influential biodiesel standards, ASTM 

D6751 in the USA and EN 14214 in the EU, are 

Biodiesel from alternative oilseed feedstocks: 

camelina and field pennycress

Bryan R Moser*

Biodiesel is prepared from lipids by transesterification with a monohydric alcohol and may serve as a 

replacement or blend component for conventional petroleum diesel fuel (petrodiesel). Advantages of 

biodiesel over petrodiesel include strongly positive energy balance, domestic and renewable origin, 

enhanced lubricity and biodegradability, superior flash point, negligible sulfur and aromatics content, and 

low environmental toxicity. However, high feedstock cost, reduced storage and oxidative stability, inferior 

volumetric energy content and poor cold-flow properties represent critical technical deficiencies relative 

to petrodiesel. This review covers biodiesel standards, production and optimum reaction conditions, the 

influence of free fatty acids on production, the influence of composition on fuel properties and traditional 

feedstocks. A particular emphasis is placed on the alternative oilseed feedstocks camelina (Camelina sativa) 

and field pennycress (Thlaspi arvense) as promising nonfood candidates with high oil contents that would 

not displace existing agricultural production and would flourish in temperate climates.

 Review

*Bio-Oils Research Unit, National Center for Agricultural Utilization Research, Agricultural Research Service, United States Department of Agriculture, 

1815 North University Street, Peoria, IL 61604, USA

Tel.: +1 309 681 6511; Fax: +1 309 681 6524; E-mail: bryan.moser@ars.usda.gov

Biofuels (2012) 3(2), 193–209
194 Biofuels (2012) 3(2) future science group

 Review Moser

summarized in Tables 1 & 2, respectively. An additional ASTM standard 

covering blends of biodiesel from 6 

to 20 vol% in petrodiesel, ASTM 

D7467, is summarized in Table  3. 

The US and European petrodiesel 

standards ASTM D975 and EN 590 

permit up to 5 and 7 vol% biodiesel 

(B5 and B7), respectively. Biodiesel 

is approved for use as heating oil in 

both the EU and the USA, and is 

covered by ASTM D396 (up to B5) 

and EN 14213 (B100). Biodiesel 

certified as compliant with ASTM 

D6751 may be used as a blending 

component in ASTM D7467, D975 

and D396. Correspondingly, biodiesel must meet the specifications of 

EN 14214 in the EU before inclusion in petrodiesel, as mandated by 

EN 590.

The European biodiesel standard, EN 14214, states that biodiesel is to be comprised 

of FAMEs, thus excluding other alkyl esters. In addition, specifications such as iodine value, linolenic acid 

methyl ester content and polyunsaturated FAME content (Table 2) in EN 14214 limits feedstock choice for 

biodiesel production. ASTM D6751 defines biodiesel as 

monoalkyl esters prepared from vegetable oils or animal 

fats, thereby inadvertently excluding other lipid sources 

such as algae. Under consideration for future versions of 

ASTM D6751 is a change in phrasing that would ameliorate this oversight. The official definition of biodiesel 

in ASTM D6751 ensures that critical moieties for fuel 

performance, such as monoalkyl esters and long-chain 

FAs, are included. Monoalkyl esters are specified because 

they impart favorable antiwear and biodegradability 

properties to biodiesel. Esters also ensure that kinematic 

viscosity (KV) (40°C) will be within the specified range. 

The long-chain FA requirement increases the probability 

that cetane numbers (CNs) will be above the minimum 

specified limit. Additionally, ASTM D6751 does not 

contain limits on iodine value, linolenic acid methyl ester 

content and polyunsaturated FAME content. Instead, 

fuel performance-based test methods are emphasized. 

However, it should be noted that EN 14214 contains 

the same performance-based specifications. Both ASTM 

D6751 and EN 14214 recommend that antioxidants be 

added to biodiesel immediately after its production to 

maintain stability.

Table 1. American Society for Testing and Materials D6751biodiesel standard.

Property Test method(s) Limits Units

Flash point (closed cup) ASTM D93 93 min oC

Alcohol control;

One of the following shall be met:

Methanol content EN 14110 0.2 max % mass 

Flash point ASTM D93 130 min oC

Water and sediment ASTM D2709 0.050 max % volume

Kinematic viscosity (40°C) ASTM D445 1.9–6.0 mm2

/s

Sulfated ash ASTM D874 0.020 max % mass

Sulfur ASTM D5453 15 max ppm

Copper strip corrosion ASTM D130 3 max

Cetane number ASTM D613 47 min

Cloud point ASTM D2500 Report oC

Cold soak filterability ASTM D7501 360 max seconds

Carbon residue ASTM D4530 0.050 max % mass

Acid number ASTM D664 0.50 max mg KOH/g

Free glycerin ASTM D6584 0.020 max % mass

Total glycerin ASTM D6584 0.240 max % mass

Oxidation stability EN 15751 3.0 min hours

Phosphorous content ASTM D4951 0.001 max % mass

Na plus K EN 14538 5 max ppm

Ca plus Mg EN 14538 5 max ppm

Distillation temperature, 

atmospheric equivalent temperature 

90% recovered

ASTM D1160 360 max oC

ASTM: American Society for Testing and Materials; EN: European Standard; max: Maximum; min: Minimum.

Key terms

Camelina (Camelina sativa): Also 

known as false flax or gold-of-pleasure, 

is a broadleaf oilseed flowering plant of 

the Brassicaceae family that grows 

optimally in temperate climates and is 

native to Eurasia. The seed oil content, 

along with various agronomic 

characteristics, renders it attractive as 

an alternative feedstock for production 

of biodiesel.

Field pennycress (Thlaspi arvense): Also 

known as stinkweed or Frenchweed, is a 

winter annual belonging to the 

Brassicaceae family that is native to 

Eurasia but distributed throughout the 

world as a weed. With high seed oil 

content and favorable agronomics, it is 

an attractive nonfood alternative source 

of biodiesel. 

Transesterification: Chemical process 

by which lipids are converted into 

biodiesel by treatment with a 

monohydric alcohol and catalyst at 

elevated temperature.
Biodiesel from alternative oilseed feedstocks Review

future science group www.future-science.com 195

Advantages & disadvantages

Miscible with petrodiesel in any 

proportion, biodiesel has numerous 

technical advantages over ultra-low 

sulfur diesel (<15 ppm S) fuel, which 

include: inherently good lubricity, 

low toxicity, domestic origin and 

production, derivation from renewable feedstocks, higher flash point 

(safer handling), superior biodegradability, negligible sulfur and 

aromatics content, strongly positive 

energy balance and lower overall 

exhaust emissions [1–3]. In addition, 

biodiesel produced from soybean 

oil as well as waste greases, oils and 

fats meets or exceeds the required 

minimum GHG reduction standards defined by the Renewable 

Fuels Standard (RFS2) in the USA 

[4]. Important disadvantages relative 

to ultra-low sulfur diesel include: 

comparatively high feedstock cost, 

limited feedstock availability, inferior storage and oxidative stability, 

lower volumetric energy content, 

susceptibility to hydrolysis as well 

as microbial degradation, inferior 

cold flow properties and in some 

cases higher nitrogen oxides (NOx) 

exhaust emissions [1–3]. Many of 

the deficiencies of biodiesel may 

be mitigated through cold-flow 

improver [5–7] and antioxidant [8–11]

additives, along with blending with 

petrodiesel [5,10–13] and proper storage coupled with reduced storage 

time [13–15]. Additional methods 

to enhance cold-flow properties 

of biodiesel include crystallization fractionation (winterization) [16,17] and transesterification with long- or 

branched-chain monohydric alcohols [18,19]. Strategies to 

improve exhaust emissions include after-treatment technologies such as selective catalytic reduction, exhaust 

gas recirculation, diesel oxidation catalysts and NOx or 

diesel particulate filters [20–22]. 

Feedstock acquisition may account for up to 88% of 

production costs when biodiesel is prepared from refined 

commodity oils [23–25]. A promising solution to the costprohibitive issue of high feedstock cost is employment of 

alternative feedstocks of lesser value such as soapstocks, 

acid oils, tall oils, used cooking oils and waste restaurant 

greases, various animal fats, nonfood plant oils, and 

oils obtained from selected trees and shrubs. However, 

many low-value feedstocks may 

contain prohibitively high levels of 

FFAs, water and/or insoluble matter, which negatively impact conventional production of biodiesel 

by homogenous alkaline catalysts if 

not removed beforehand [26]. 

Energy balance

The net energy ratio (NER) is the 

amount of output energy divided by 

the needed input energy, and values 

greater than 1.0 are indicative of a 

positive energy balance (i.e., more 

energy is available than was required 

Table 2. EN 14214 biodiesel standard.

Property Test method(s) Limits Units

Fatty acid methyl ester content EN 14103 96.5 min % (mol/mol)

Density (15°C) EN ISO 3675, 

EN ISO 12185 

860–900 kg/m3

Kinematic viscosity (40°C) EN ISO 3104 3.50–5.00 mm2/s

Flash point EN ISO 2719,

EN ISO 3679

101 min oC

Sulfur content EN ISO 20846,

EN ISO 20884

10.0 max mg/kg

Carbon residue 

(10% distillation residue)

EN ISO 10370 0.30 max % (mol/mol)

Cetane number EN ISO 5165 51.0 min

Sulfated ash content ISO 3987 0.02 max % (mol/mol)

Water content EN ISO 12937 500 max mg/kg

Total contamination EN 12662 24 max mg/kg

Copper strip corrosion 

(3 h at 50°C)

EN ISO 2160 Class 1 Degree of corrosion

Oxidation stability (110°C) EN 15751 6.0 min h

Cold filter plugging point EN 116 Variable oC

Acid value EN 14104 0.50 max mg KOH/g

Iodine value EN 14111 120 max g I2

/100 g

Linolenic acid methyl ester content EN 14103 12.0 max % (mol/mol)

Polyunsaturated 

(≥four double bonds) methyl esters

EN 14103 1 max % (mol/mol)

Methanol content EN 14110 0.20 max % (mol/mol)

Monoacylglycerol content EN 14105 0.80 max % (mol/mol)

Diacylglycerol content EN 14105 0.20 max % (mol/mol)

Triacylglycerol content EN 14105 0.20 max % (mol/mol)

Free glycerol EN 14105

EN 14106

0.02 max % (mol/mol)

Total glycerol EN 14105 0.25 max % (mol/mol)

Group I metals (Na and K) EN 14108

EN 14109

EN 14538

5.0 max mg/kg

Group II metals (Ca and Mg) EN 14538 5.0 max mg/kg

Phosphorous content EN 14107 4.0 max mg/kg

EN: European Standard; max: Maximum; min: Minimum.

Key terms

Fatty acid methyl ester: Also known as 

biodiesel, a methyl ester of a long-chain 

fatty acid normally produced during 

transesterification of plant oils or 

animal fats. 

Alternative feedstock: Source of 

low-cost nonfood lipids for sustainable 

production of biodiesel with high oil 

content that ideally does not displace 

existing agricultural production. 

Commodity oils/fats represent 

traditional (or 1st generation) feedstocks 

but have competing food-related 

applications and are generally 

prohibitively expensive. 
196 Biofuels (2012) 3(2) future science group

 Review Moser

for production). Life cycle assessments of biodiesel prepared from soybean [3], palm [27] and sunflower [28] oils 

have yielded NERs of 4.5:1, 4.8:1 and 4.5:1, respectively. Differences in agricultural practices and other 

inputs are responsible for the variability of NER among 

feedstocks. Even within a given feedstock NER may 

vary, depending on the inputs and outputs selected for 

inclusion. For instance, NERs of 0.79:1 [29], 1.93:1 [30]

and 3.21:1 [31] were reported for biodiesel prepared from 

soybean oil. The lowest value (0.79:1) was debunked by 

a subsequent study [32]. The NER of 4.5:1 reported by 

Pradhan et al. [3] represents an update to the Sheehan et 

al. [31] study (3.2:1) by taking into consideration technological advancements in agricultural practices, biodiesel 

production, pesticide use, and soybean yield and genetics. For comparison, the NER of petrodiesel is reported 

as 0.83:1 due to the high energy inputs required for 

extraction of crude oil from the Earth, transportation of 

crude oil across vast distances from oil fields to refinery 

locations and energy requirements of crude oil refinery 

operations [31]. 

Production of biodiesel

Biodiesel is produced via the transesterification reaction, whereby triacylglycerols (TAGs) react with shortchain monohydric alcohols with assistance provided by 

a homogeneous alkaline catalyst at elevated temperature 

to yield FA alkyl esters (FAAEs) and the co-product 

glycerol (Figure 1). In most cases methanol is used as a 

co-reactant, since it is normally the 

least expensive of the short-chain 

monohydric alcohols. In regions such 

as Brazil, where sugarcane is plentiful, ethanol is utilized to produce FA 

ethyl esters (FAEEs) because it is less 

expensive than methanol and widely 

available. Ethanol also has the added 

benefit of being bioderived when 

produced from fermentation of sugars, whereas methanol, on an industrial scale, is produced from natural 

gas (methane). 

Industrially, feedstock, alcohol 

and catalyst are mixed in continuously stirred tank reactors (CSTRs) 

until the reaction has reached equilibrium [33]. Excess alcohol is used 

to drive the equilibrium toward 

the products (FAAEs). Often, two 

CSTRs are utilized in series (with 

glycerol removal in between) to 

ensure a high level of conversion 

to FAAEs. The alkaline catalyst is 

dissolved in the alcohol co-reactant 

prior to its addition to the CSTR containing the plant 

oil or animal fat to minimize the possibility that a concentrated region of catalyst might come into contact with 

TAGs and promote unwanted soap formation. Separation 

of glycerol and biodiesel at the conclusion of the reaction 

is accomplished with a settling tank or with a disk centrifuge. The glycerol stream is then acidified to neutralize 

residual catalyst and to decompose soaps into FFAs and 

inorganic salts. Alcohol entrained in the glycerol phase 

can be recycled through an evaporative process. The fraction containing FAAEs is also neutralized with acid, and 

alcohol is recovered, followed by washing with water and 

subsequent drying to provide the finished biodiesel product. Figure 2 provides a schematic depiction of traditional 

industrial biodiesel production. 

The most significant parameters that determine 

compatibility of plant oils or fats with the traditional 

homogenous alkaline-catalyzed transesterification procedure (Figure 2) are FFAs and water content (Figure 3). 

Typically, refined lipids contain very low percentages of 

FFAs (<0.05 wt%) and water (< 0.1 wt%) [34], so their 

direct conversion to biodiesel is readily accomplished. 

Crude lipids may have considerably higher percentages 

of these contaminants, so purification is required prior 

to the conventional homogenous, alkaline-catalyzed 

transesterification procedure depicted in Figure 2. Water 

and FFA content can be reduced with physical refining [34]. Additionally, FFAs can be esterified to FAAEs 

prior to methanolysis to mitigate yield loss [2,25,26]. 

Table 3. American Society for Testing and Materials D7467 biodiesel–petrodiesel blend 

(B6–B20) standard.

Property Test method(s) Limits Units

Biodiesel content ASTM D7371 6–20 % volume

Flash point (closed cup) ASTM D93 52 min °C

One of the following must be met:

Cetane index

ASTM D976 40 min

Aromaticity ASTM D1319 35 max % volume

Water and sediment ASTM D2709 0.050 max % volume

Kinematic viscosity (40°C) ASTM D445 1.9–4.1 mm2

/s

Sulfur content ASTM D5453 15 max ppm

Copper strip corrosion ASTM D130 3 max

Cetane number ASTM D613 40 min

Ramsbottom carbon residue ASTM D524 0.35 max % mass

Acid value ASTM D664 0.30 max mg KOH/g

Oxidation stability EN 14112 6.0 min h

Ash content ASTM D482 0.01 max % mass

Lubricity (HFRR, 60°C) ASTM D6079 520 max mm

Cloud point or

LTFT/CFPP

ASTM D2500, 

D4539, D6371

Only guidance 

provided

°C

Distillation temperature 

(90% recovered)

ASTM D86 343 max °C

ASTM: American Society for Testing and Materials; CFPP: Cold filter plugging point; EN: European Standard; 

HFRR: High-frequency reciprocating rig; LTFT: Low temperature flow test; max: Maximum; min: Minimum.
Biodiesel from alternative oilseed feedstocks Review

future science group www.future-science.com 197

Optimum reaction conditions

In a seminal paper published in 1984, Freedman et al.

elucidated the classic homogenous, alkaline-catalyzed 

reaction conditions for the methanolysis of anhydrous, low-FFA (<0.50 wt%) TAGs to provide FAMEs 

and glycerol in an essentially quantitative yield [35]. 

Freedman et al. reported that a 6:1 molar ratio of methanol to TAG, 0.5 wt% homogenous alkaline catalyst (with 

respect to TAG), 600+ rpm agitation intensity and 1 h 

of reaction at 60°C produced FAMEs in high yields [35]. 

Numerous subsequent studies performed on a wide variety of refined feedstock oils have essentially verified the 

optimum reaction conditions reported by Freedman et 

al., utilizing modern statistical methods such as response 

surface methodology (RSM) [36,37]. Reaction parameters 

normally investigated using RSM to give maximum yield 

of biodiesel include catalyst type and amount, reaction 

time and temperature and molar ratio of alcohol to 

oil. A representative recent example of reaction conditions optimized by RSM is the work of Rashid et al., in 

which sunflower oil methyl esters were prepared using 

0.70 wt% KOH, at 50°C for 65 min with a molar ratio of 

methanol to oil of 6:1 to provide biodiesel in greater than 

91% yield [37]. As seen by comparison of the conditions 

elucidated by Freedman et al. to that of the example, 

the reaction conditions do not vary significantly after 

optimization by RSM.

Influence of FFAs

Feedstocks containing a significant percentage of FFAs 

(>2 wt%) will render typical homogenous alkaline 

catalysts ineffective due to a deleterious side reaction 

(Figure 3) in which the catalyst reacts with FFAs to produce unwanted soap (sodium salt of FA) and water (or 

methanol in the case of sodium methoxide). Ultimately, 

reaction with FFAs deactivates the catalyst and significantly reduces biodiesel yield [2,26,33,38–44]. In fact, alkaline-catalyzed transesterification will not occur at all, or 

will be significantly retarded, if the FFA content of the 

feedstock is 3 wt% or greater [40,41]. Numerous studies 

reported that homogenous, alkaline-catalyzed methanolysis proceeds optimally when FFA content is below 

0.50 wt% [35,40,45]. However, the yield of biodiesel plummets to 6% with an increase in FFA content to 5.3 wt% 

[43]. A further complicating factor of high FFA content 

is the production of water upon reaction with alkaline hydroxide catalysts (Figure 3). Water is particularly 

problematic because, in the presence of any remaining 

catalyst, it can hydrolyze biodiesel to produce additional 

FFAs and methanol (Figure 3) [42]. Sodium and potassium 

salts of FFAs (soaps) also promote dissolution of FAMEs 

into the glycerolic phase during purification, thus further suppressing the final yield of biodiesel [46,47]. If the 

percentage of FFAs is high enough, phase separation at 

the conclusion of methanolysis will not be possible [47]. 

Lastly, increasing the concentration of alkaline catalyst 

to counteract the effect of catalyst deactivation by FFAs 

is detrimental, as such a strategy merely accelerates 

unwanted hydrolysis of TAGs and FAEEs [46].

In cases where FFA content is prohibitively high for 

direct conversion of lipids to FAMEs a two-step procedure is employed, whereby acid pretreatment is followed 

by transesterification with homogenous alkaline catalysts 

to produce FAMEs. Acid-catalyzed esterification of FFAs 

to FAMEs is normally conducted in the presence of heat, 

excess methanol and a catalytic amount of sulfuric acid 

[2,40,41,43,48–51]. This two-step procedure readily accommodates high FFA-containing, low-cost feedstocks for 

the preparation of biodiesel [40,41]. Despite the additional 

fixed capital and operational costs, the integrated twostep procedure is being increasingly applied industrially to prepare biodiesel from low-cost but high FFAcontaining feedstocks [38]. As previously discussed, 

feedstock cost dictates biodiesel process economics, so 

less expensive but lower quality feedstocks may offset 

the increased capital investment in a dual-step facility. 

Several studies have conducted RSM-optimized 

methanolysis on acid-pretreated oils and verified that 

the reaction conditions do not vary significantly from 

those reported by Freedman et al. [35]. An advantage to 

esterification of FFAs as opposed to their removal by 

refining is that the yield of biodiesel is higher in the 

two-step case of esterification/transesterification because 

FAs are not removed from the system. Instead, they are 

converted into the desired product. 

O O

O

R

O

R

O

R

O

+ 3R'OH R OR'

O

TAG Alcohol

Glycerol

O OH

O

R

O

R

O

DAG

+

R OR'

O

HO OH

O

R

O

MAG +

R OR'

O

HO OH

OH

+

R'= −CH3 (normally)

R OR'

O

= biodiesel

k1

k2

k3 k4

k k6 5

Figure 1. Transesterification of triacylglycerols to fatty acid alkyl esters 

(biodiesel) and glycerol.

 DAG: Diacylglycerol; MAG: Monoacylglycerol; TAG: Triacylglycerol.
198 Biofuels (2012) 3(2) future science group

 Review Moser

Phase distribution during methanolysis

Because TAGs are not soluble in methanol, methanolysis 

commences as two immiscible phases [52–54]. Illustrative 

of this is the fact that only 5.7 g of soybean oil is soluble 

in 1 l of methanol at 30°C with vigorous agitation. 

With an increase in temperature 

to 40°C, the solubility of soybean 

oil increases to 7.5 g after vigorous 

agitation [54]. The alkaline catalyst 

is exclusively dissolved in the polar 

methanol phase at the onset of 

methanolysis and only interacts with 

TAGs at the interface of the phases 

unless sufficient agitation is introduced [52,53]. Stirring of adequate 

intensity causes TAG transport into 

the methanol phase where they are 

rapidly converted into FAMEs and 

glycerol (Figure 1). Once the diacylglycerol (DAG) and monoacylglycerol 

(MAG) intermediates are formed 

in sufficient quantity, they act as 

emulsifiers to improve mass transfer 

of TAGs into the methanolic phase. 

When near completion, methanolysis transforms into another biphasic 

system that consists of ester-rich 

(FAME) and glycerol-rich phases. 

At this stage, catalyst and methanol are preferentially soluble in the 

more polar glycerolic phase [52,55]. 

The phases readily partition once 

the reaction is complete and agitation is ceased, which facilitates 

purification of FAMEs. Zhou and 

Boocock demonstrated that 42.0% 

of residual methanol was located in 

the FAME-rich phase, whereas the 

remaining 58.0% was in the glycerolic phase. Additionally, 94.2% of 

sodium methoxide catalyst was in 

the glycerolic phase. As expected, 

97.7% of glycerol partitioned into 

the denser glycerolic phase and 

99.0% of FAMEs separated into the 

ester-rich phase [53]. 

Chemical structure & 

common FAs

The chemical structure of biodiesel 

(FAMEs) consists of methanol esterified to FAs. The FA moiety is derived 

from TAGs, which are triesters of 

glycerol with three FAs attached 

via ester linkages to the glycerol backbone (Figure 1). 

Palmitic (hexadecanoic), stearic (octadecanoic), oleic 

(9Z-octadecenoic), linoleic (9Z,12Z-octadecadienoic) 

and linolenic (9Z,12Z,15Z-octadecatrienoic) acids are 

the five most commonly encountered FAs in plant oils 

[1,2,56]. However, other FAs are occasionally encountered in significant quantities in a limited number of 

plant oils. For instance, erucic (13Z-docosenoic) acid 

is an important constituent in plant oils from the 

Brassicaceae family, of which wild mustard [57] and 

high-erucic acid rapeseed oil are examples. Other examples include capric (decanoic) acid-containing cuphea 

(Cuphea viscosissima x Cuphea lanceolata) [58] oil, lauric 

CSTR

#1

Oil Methanol

Catalyst

Separator

Crude

FAME

Neutralization

Acidification Acid

FFA

Crude glycerol

Methanol

removal

Methanol

removal

Glycerol, ∼85%

Distillation

Wet methanol

Wet methanol

Methanol

Water

Water

wash

Dirty

water Water

Dryer

Biodiesel

CSTR

#2

Catalyst

Methanol

Salts

Separator

Crude FAME

Figure 2. Industrial production of biodiesel from feedstocks with low free fatty acids 

and water content. Depicted are two CSTRs in sequence with glycerol removal in between. 

Methanol recovered after distillation can be recycled. 

CSTR: Continuously stirred tank reactor; FAME: Fatty acid methyl ester; FFA: Free fatty acid.

Key term

Brassicaceae: Herbaceous family of 

flowering plants with high seed oil 

content that is generally compatible 

with fallow lands. Widely distributed 

throughout the northern temperate 

climate zone and includes rapeseed/

canola. 
Biodiesel from alternative oilseed feedstocks Review

future science group www.future-science.com 199

(dodecanoic) acid-containing coconut [59], palm kernel 

[60] and babassu [60] oils, petroselenic (6Z-octadecenoic) 

acid-containing coriander (Coriandum sativum) oil 

[49], and 5Z-eicosenoic acid-containing meadowfoam (Limnanthes alba) oil [61]. Listed in Table 4 is the 

distribution of common FAs encountered in plant oils.

Influence of chemical structure on fuel 

properties

Fuel properties of biodiesel are largely determined by 

FA composition, with other factors such as presence 

of contaminants and minor components playing lesser 

roles [2,56,62]. As a result, fuel properties of biodiesel vary 

depending on FA composition. Such dependence of fuel 

properties on chemical structure may inform genetic 

modification of oilseed crops for optimum composition 

to yield the most favorable biodiesel fuel properties [63]. 

Fuel properties directly impacted by FA composition 

include low cold-flow properties, oxidative stability, 

KV and CN [1,2,56,62]. Minor components in biodiesel and feedstock lipids are defined as naturally occurring nonpolar unsaponifiable species and may include 

tocopherols, tocotrienols, phospholipids, steryl glucosides, wax esters, chlorophyll, fat soluble vitamins and 

hydrocarbons (such as squalene, carotenes and polycyclic aromatic hydrocarbons) [34,64,65]. Contaminants 

in biodiesel are defined as transesterification and may 

include FFAs, soaps, TAGs, DAGs, MAGs, alcohol, 

catalyst, salts, glycerol, metals and water. 

The cold-flow properties of biodiesel are impacted 

by chain length, degree of unsaturation, double-bond 

geometry and ester head group. As seen in Table 5, higher 

melting points (MPs) are obtained as the chain length 

of saturated FAMEs is extended (C12:0, MP 4.3°C; 

C18:0, MP 37.7°C) [66]. Compounds of identical chain 

length exhibit progressively lower MPs as the content 

of double bonds increases, as evidenced by the MPs of 

C18:0 (37.7°C), C18:1 (-20.1°C), C18:2 (-43.1°C) and 

C18:3 (-52°C) [66]. Double-bond geometry is another 

important factor influencing MP. The orientation of 

double bonds in nearly all natural oils is the cis- configuration. However, trans-isomers may be chemically 

introduced through catalytic partial hydrogenation or 

unnatural other means [67,68]. Isomerization to the transconfiguration results in a modified 3D geometry that is 

manifested by higher MPs relative to the corresponding cis-isomers. Illustrative of this is a comparison of 

the MPs of methyl elaidate (methyl 9E-octadenenoate) 

and methyl oleate, which are 9.9 and -20.1°C, respectively [66]. The influence of ester head group on MP is 

illustrated by methyl, ethyl, propyl and butyl esters of 

stearic acid, which have MPs of 37.7, 33.0, 28.1 and 

25.6°C, respectively [66]. In general, FAEEs exhibit 

lower MPs as the number of carbons (up to eight) in 

the ester head group is increased. Because biodiesel is 

a mixture of FAAEs with a wide range of MPs, initial 

crystal growth that occurs upon cooling of biodiesel to 

sub-ambient conditions is primarily caused by crystallization of higher melting constituents [16]. As mentioned 

previously, alkyl esters other than methyl do not qualify 

as biodiesel according to EN 14214. 

Oxidative stability of biodiesel is principally influenced by degree of unsaturation (number of double 

bonds), with factors such as double-bond location 

and geometry also playing roles. The rate of autoxidation primarily depends on the number and location of 

methylene-interrupted double bonds contained within 

the hydrocarbon backbone of FAAEs. Bis-allylic methylene positions found in methyl linoleate (carbon 11) 

and methyl linolenate (carbons 11 and 14) contain 

C-H bonds with lower dissociation energies (more 

labile hydrogens), and are, therefore, considerably more 

prone to hydrogen abstraction than allylic, especially 

saturated methylene positions. FAAEs with a higher 

+ NaOH

(or NaOCH3

) R OH

O

R O−Na+

O

+ H2

O

(or CH3

OH)

FFA Soap

R OCH3

O

Biodiesel

+ H2

O + CH3

OH R OH

O

FFA

[2]

[1]

Figure 3. Deleterious side reactions caused by the 

presence of water and free fatty acids. Hydrolysis 

of biodiesel (reaction 1) to yield FFAs and methanol. 

Formation of soap from reaction of FFAs with alkali 

catalyst (reaction 2).

FFA: Free fatty acid.

Table 4. Systematic, common and shorthand names of fatty acids in 

biodiesel feedstocks.

Systematic Common Shorthand

Decanoic Capric C10:0

Dodecanoic Lauric C12:0

Tetradecanoic Myristic C14:0

Hexadecanoic Palmitic C16:0

9Z-hexadecenoic Palmitoleic C16:1 9c

Octadecanoic Stearic C18:0

9Z-octadecenoic Oleic C18:1 9c

9Z,12Z-octadecadienoic Linoleic C18:2 9, 12c

9Z,12Z,15Z-octadecatrienoic Linolenic C18:3 9, 12, 15c

Eicosanoic Arachidic C20:0

11Z-eicosenoic Gadoleic C20:1 11c

Docosanoic Behenic C22:0

13Z-docosenoic Erucic C22:1 13c

Tetracosanoic Lignoceric C24:0
200 Biofuels (2012) 3(2) future science group

 Review Moser

number of methylene carbons allylic to double bonds 

are vulnerable to autoxidation. Particularly susceptible 

to autoxidation are bis-allylic methylene positions, as 

evidenced by relative rates of oxidation of 1, 41 and 98 

for ethyl esters of oleic (2 methylene positions), linoleic 

(2 methylene and 1 bis-allylic position), and linolenic (2 

methylene and 2 bis-allylic positions) acids, respectively 

[69]. In another report, the relative rate of oxidation is 

reported as 1, 27 and 77, respectively [70]. These results 

are confirmed by examination of the induction periods (IPs) (EN 14112, 110°C) (Table 5) of methyl esters 

of stearic (>40 h), oleic (2.5 h), linoleic (1.0 h) and 

linolenic (0.2 h) acids [71]. Autoxidation commences 

with production of resonance-stabilized alkyl radicals 

through allylic hydrogen abstraction caused by an 

initiator (e.g., heat, light, metals and peroxides) [72]. 

Consequently, superior oxidative stability is generally 

observed in biodiesel prepared from feedstocks with 

relatively high saturated FA content and/or relatively 

low polyunsaturated FA content. 

The effect of double-bond location on oxidative stability is evidenced by comparison of the IPs (110°C) 

of methyl petroselinate (IP = 3.5 h) and methyl oleate (IP = 2.5 h) [71]. Analogously, methyl 5Z-eicosenate 

(IP = 69.4 h) is considerably more stable to oxidation 

than methyl oleate (IP = 14.8 h) at 90°C [73]. It would 

stand to reason that biodiesel fuels enriched in FAMEs 

with unsaturation located close to the ester head group 

would have superior oxidative stability relative to the 

more typical 9-ene FAMEs. This supposition is verified 

by comparison of FAMEs prepared from coriander and 

meadowfoam oils to soybean oil methyl esters (SME). 

Methyl esters prepared from meadowfoam oil, which is 

enriched in up to 64.2 wt% 5Z-eicosenoic acid, has an 

IP (110°C) of 66.9 h [61]. The IP (110°C) of coriander oil 

methyl esters, which is enriched in >68% petroselenic 

acid, is 14.6 versus 5.0 h for SME [49].

Double-bond geometry (cis- vs trans-isomers) 

impacts oxidative stability, which is illustrated by the 

contrasting IPs of FAMEs of oleic (2.5 h) and elaidic 

(7.7 h) acids [71]. Trans-isomers are thermodynamically 

more stable than the corresponding cis-isomers, which 

explains their enhanced oxidative stability relative to 

cis-isomers. Biodiesel fuels that contain trans-FAAEs 

exhibit higher oxidative stability than those with a similar number of entirely cis double bonds. For instance, 

partially hydrogenated SME (7.7% trans-FAME, 16.4% 

saturated FAME and 44.7% polyunsaturated FAME) 

yielded an IP of 6.2 h (110°C) versus 2.3 h for SME (0% 

trans, 16.9% saturated and 59.8% polyunsaturated) [67]. 

Chain length and degree of unsaturation principally 

affect KV of FAMEs. As seen in Table 5, KV increases 

with increasing chain length among otherwise similar 

constituents. For instance, saturated FAMEs of lauric (C12:0), myristic (C14:0), palmitic (C16:0) and 

stearic (C18:0) acids have KVs of 2.43, 3.30, 4.38 

and 5.85 mm2/s, respectively. Lower KVs are observed 

with increasing double-bond content among otherwise 

similar constituents, as noted by the FAMEs of stearic 

(C18:0, 5.85 mm2/s), oleic (C18:1, 4.51 mm2/s), linoleic 

(C18:2, 3.65 mm2/s) and linolenic (C18:3, 3.14 mm2/s) 

acids. Double-bond orientation also impacts KV, 

which is illustrated by comparison of methyl elaidate 

(5.86 mm2/s) and methyl linoelaidate (5.33 mm2/s; 

methyl 9E, 12E-octadecadienoate) to the corresponding 

cis-isomers (methyl oleate and linoleate) [74]. 

KV is strongly temperature dependent, as higher KVs 

are reliably observed as the temperature of measurement 

is incrementally decreased [48,75–78]. For instance, an 

increase in the KV of SME from 4.15 to 11.75 mm2/s 

is observed as the temperature is lowered in 10°C increments from 40 to 0°C [74]. In addition, the KV of field 

pennycress oil methyl esters increases from 5.24 mm2/s 

at 40°C to 8.65 mm2/s at 20°C, 16.70 mm2/s at 0°C and 

35.52 mm2/s at -10°C [48]. Similar results are obtained 

with low sulfur (30 ppm S) diesel fuel, with values of 

2.90, 3.64, 4.55, 6.21 and 8.58 mm2

/s at 40, 30, 20, 10 

and 0°C, respectively [76]. Increased viscosity of biodiesel 

at low (subambient) temperatures is of concern because 

Table 5. Fuel properties of fatty acid alkyl esters 

commonly found in biodiesel. 

Fatty acid ethyl 

esters

MP†

(

oC)

KV‡

(mm2/s)

IP§

(h)

CN¶

C12:0 ME 4.3 2.43 >40 67

C12:0 EE -1.8 2.63 # #

C14:0 ME 18.1 3.30 >40 #

C14:0 EE 12.5 3.52 # #

C16:0 ME 28.5 4.38 >40 86

C16:0 EE 23.2 4.57 # 93

C16:1 ME -34.1 3.67 2.1 51

C16:1 EE -36.7 # # #

C18:0 ME 37.7 5.85 >40 101

C18:0 EE 33.0 5.92 >40 97

C18:0 BE 25.6 7.59 # 92

C18:1 ME -20.1 4.51 2.5 59

C18:1 EE -20.3 4.78 3.5 68

C18:1 BE -34.8 5.69 # 62

C18:2 ME -43.1 3.65 1.0 38

C18:2 EE -56.7 4.25 1.1 40

C18:3 ME -52 3.14 0.2 23

C18:3 EE -61.7 3.42 0.2 27

†

Data from [92]. ‡

Data from [100]. §

Data from [97]. ¶

Data from [106]. #

Not determined or reported.

BE: Butyl ester; CN: Cetane number; EE: Ethyl ester; IP: Induction period; 

KV: Kinematic viscosity; ME: Methyl ester; MP: Melting point.
Biodiesel from alternative oilseed feedstocks Review

future science group www.future-science.com 201

it may cause potentially excessive fuel injection pressures during initial engine warm-up. Furthermore, fuel 

starvation of diesel engines may result as the biodiesel 

fuel moves more slowly through filters and fuel lines at 

subambient temperatures [76,78]. Several methodologies 

to predict KV of biodiesel based on FAAE composition 

are reported. These procedures essentially consist of a 

weighted average method utilizing the FA composition 

and KVs of individual FAAEs to provide a calculated 

KV [75,78]. Lastly, the blend percentage of biodiesel in 

petrodiesel can be determined from KV if the values for 

neat biodiesel and petrodiesel are known [77]. 

CN is a dimensionless measure of diesel fuel ignition 

performance and is obtained by comparing it to reference fuels in a standardized engine test. As a primary 

indicator of diesel fuel quality, CN is directly related to 

the ignition delay diesel fuels experience upon injection 

into combustion chambers of diesel engines. Ignition 

delay is defined as the period of time, expressed in 

degrees of crank angle rotation, between the start of 

fuel injection and the start of combustion. Higher CNs 

are observed with shorter ignition delay and vice versa. 

Hexadecane, trivially referred to as cetane, is arbitrarily 

assigned a CN of 100 and is the high-quality reference 

standard of the cetane scale. At the other end of the 

cetane scale is 2,2,4,4,6,8,8-heptamethylnonane, which 

has a long ignition delay time and an arbitrarily assigned 

CN of 15. Typical CN testing is in the range of 30 to 

65. CN is conceptually similar to octane number (ON) 

and fuels with low CNs will have high ONs, and vice 

versa. As evidenced by the end points of the CN scale, 

branching reduces CN. Other factors influencing CN 

include chain length and degree of unsaturation, with 

higher CNs observed for longer chain compounds and 

those with lower degrees of unsaturation. Illustrative of 

this is a comparison of methyl esters of lauric (67), palmitic (86) and stearic (101) acids (Table 5). Furthermore, 

methyl esters of stearic (101), oleic (59), linoleic (38) 

and linolenic (23) acids demonstrate the influence of 

unsaturation on CN [79]. 

Commercial feedstocks

A desire among liquid transportation fuel-importing countries to reduce their dependence on foreign 

sources of energy has resulted in the implementation 

of numerous governmental incentives and mandates 

for domestic production and consumption of alternative biofuels. Such policies, along with other factors, 

have resulted in a rapid increase in worldwide biodiesel production capacity. However, it does not appear 

possible to meet the increased production capacity and 

mandated demand with traditional sources of biodiesel prepared from commodity lipids. For example, it 

is estimated that if all US soybean production were 

dedicated to biodiesel, only 6% of 

diesel demand would be satisfied 

[30]. The US Energy Information 

Administration estimates that 

1.170 billion l of biodiesel was produced in the USA in 2010, versus 

34 million l in 2001 [201]. Production peaked in 2008 

at 2.567 billion l. For 2011, production is expected to 

show a rebound to a level near the historical high, owing 

to retroactive reinstatement of the lapsed US$1.00 per 

gallon biodiesel tax credit by the US Federal government. The US Energy Policy Act of 2005 included an 

RFS1 that mandated 28 million l of renewable fuels 

be blended into energy supplies by the end of 2012. 

The Energy Independence and Security Act of 2007 

(EISA) made significant changes in the structure and 

magnitude of the renewable-fuel program. The revised 

statutory requirements of EISA specify the volumes 

of cellulosic biofuel, biomass-based diesel, advanced 

biofuels, and total renewable fuel that must be used in 

transportation fuel yearly from 2010 to 2022. The EISA 

fuel program, designated RFS2, mandates the use of a 

total of 57.5 billion l per year of renewable fuel by 2012 

and 136.3 billion l per year by 2022. 

A recent report by Tilman et al. [80] identified several feedstock categories that hold the most promise as 

sources of biofuels with much lower life cycle GHG 

emissions than traditional fossil fuels and that do not 

compete with food production: perennial plants grown 

on fallow lands, crop residues, sustainably harvested 

wood and forest residues, double crops and mixed cropping systems, as well as municipal and industrial wastes. 

The four major biodiesel feedstock categories are microalgae, oilseeds, animal fats and various low-value waste 

materials such as used cooking oils, greases and soapstocks. With regard to oilseeds, desirable characteristics 

include adaptability to local growing conditions (e.g., 

rainfall, soil type and latitude), regional availability, 

high oil content, favorable FA composition, compatibility with existing farm infrastructure and practices, 

minimal agricultural inputs (water, fertilizer and pesticides), definable growth season, uniform rates of seed 

maturation, markets for co-products, compatibility 

with agriculturally undesirable lands and suitability 

for off-season rotation with conventional commodity 

crops [2,48,49,61]. Biodiesel prepared from feedstocks that 

meet all or most of the above criteria hold the greatest 

promise as alternatives to petrodiesel. 

Traditional commodity oilseed feedstocks predominately include soybean, rapeseed/canola, palm and 

sunflower oils, with lesser contributions from coconut, 

corn, cottonseed and peanut oils [2]. Also of significance are waste cooking oils derived from commodity 

lipids, as well as low-grade tallow obtained from animal 

Key term

Fallow land: Cropland that is not 

seeded for a season. May also refer to 

land that is not suitable for agricultural 

production and is thus perpetually 

fallow. 
202 Biofuels (2012) 3(2) future science group

 Review Moser

rendering. Alternative (i.e., nontraditional) feedstocks are normally 

pursued out of necessity in regions 

where more traditional plant oils 

are not locally available, as part of 

a concerted effort to reduce dependence on imported petroleum or 

because an abundance of marginal 

land is available for cultivation of 

low-input agricultural products. 

Promising alternative 

feedstocks

Algae and jatropha have attracted 

considerable interest as alternative feedstocks for production of biodiesel due to their purportedly high 

lipid densities (l/ha) [81–84]. Because of the propensity 

of jatropha to produce toxic substances, along with its 

preference for arid climates and algae’s complicated 

and expensive production and extraction systems, these 

feedstocks will not be considered here. Furthermore, the 

principal FAs in these feedstocks are fully saturated, 

which has significant deleterious implications for cold 

weather performance of the resulting biodiesel fuels 

[1,81–84]. Some strains of algae are enriched in polyunsaturated FAs, which is excellent for cold weather performance but abysmal for oxidative stability and CN, and 

is, therefore, not desirable from a fuel property standpoint. Instead, lesser-known alternatives with adaptability to temperate climate zones will be considered, such as 

camelina and field pennycress. Temperate climates are 

of particular interest because they encompass Europe, 

North America, most of Asia and portions of the Middle 

East, Africa, Australia and South America. As a result, 

the majority of the energy-consuming human population, along with our collective associated energy infrastructure, resides mostly within the temperate climate 

zones. It therefore stands to reason that energy crops 

should thrive in relatively close proximity to human 

population centers.

Members of the Brassicaceae family are particularly attractive as alternative feedstocks because they 

evolved to thrive in, and originated mostly within, the 

northern temperate climate zone [85]. Many members 

also produce seeds with high oil content and include 

commercially important species such as Brassica napus 

(rapeseed), Brassica oleracea (e.g., broccoli, cabbage and 

cauliflower), Brassica rapa (turnip), Raphanus sativus 

(common radish), Amoracia rusticana (horseradish) and 

the model organism Arabidopsis thaliana. This family of 

economically important flowering plants (Angiosperms) 

is also known as Brassicas, mustards, the crucifers or 

the cabbage family. The older scientific classification 

of the Brassicaceae was Cruciferae, which means ‘cross 

bearing’ and is descriptive of the four petals of mustard 

flowers that resemble a cross. The Brassicaceae consist 

mostly of herbaceous plants with annual, biennial or 

perennial lifespans, and includes 338 genera and 3709 

species [85]. Oilseeds derived from winter annuals are 

especially attractive feedstocks in temperate climates as 

they are often high in oil content, require few agricultural inputs, are compatible with existing farm infrastructure, can flourish on otherwise fallow land, have 

definable growth seasons and uniform seed-maturation 

rates, and can be harvested in spring, thus not displacing existing food production while simultaneously 

augmenting oil supply and providing ground cover to 

prevent soil erosion. 

Historically, members of the Brassicaceae family 

have attracted interest as cover crops for weed management due to favorable characteristics such as soil erosion mitigation, disruption of pest cycles and increased 

nutrient cycling [86]. In addition, all mustards contain 

glucosinolates, which are secondary metabolites with 

sulfur and nitrogen and are derived from glucose and an 

amino acid. Glucosinolates are not toxic but are enzymatically hydrolyzed to yield a variety of products with 

beneficial biofumigation properties, including isothiocyanates, nitriles, oxazolidinethiones, organic cyanates 

and epithionitriles. Myrosinase, the enzyme responsible 

for hydrolysis, is separated intracellularly from the glucosinolates until cellular damage occurs through events 

such as mowing, grazing, freezing, tillage or root death 

[87,88]. Although beneficial due to their biofumingation 

properties, glucosinolates, if present in sufficient concentration, may render seed meal unsuitable as a feed 

supplement for livestock animals, as higher amounts in 

feed can lead to goiter and other adverse health effects 

[86–89]. Such unsuitability may render the seed meal of 

lower monetary value while simultaneously suppressing 

the profitability of biofuels production from such crops. 

A strategy to overcome this drawback is to use low-level 

(<10%) blends of glucosinolate-containing seed meals 

in seed meals of nonglucosinolate-containing origin, to 

provide a protein source for animals with an acceptable 

level of glucosinolates while concomitantly consuming Brassicaceae seed meals. Another approach is the 

employment of glucosinolate-containing seed meals as 

biofumigants to inhibit growth of weeds, which may 

be useful to organic farmers seeking green practices for 

pest control [90,91]. 

Camelina

Camelina, also known as false flax or gold-of-pleasure, 

is a broadleaf oilseed flowering plant of the Brassicaceae 

family that grows optimally in temperate climates. 

Camelina may be grown in a variety of climatic and 

soil conditions as a spring or summer annual or as a 

Key terms

Temperate climate zones: Latitudes 

that lie between the tropics and the 

polar circles; where the majority of the 

human population resides. 

Glucosinolates: Class of secondary 

metabolites found in species of the 

Brassicaceae that contain sulfur and 

nitrogen and are derived from glucose 

and an amino acid. 

Seed meal: Solid material enriched in 

protein that is obtained when lipids are 

expelled or extracted from seeds. Seed 

meals are valuable ingredients in 

livestock feed formulations. 
Biodiesel from alternative oilseed feedstocks Review

future science group www.future-science.com 203

biannual rotational winter crop. Cultivated in Europe 

sporadically since the Bronze Age, camelina has several 

beneficial agronomic attributes: short growing season 

(85–100 days), compatibility with existing farm practices, and tolerance of cold weather, drought, semi-arid 

conditions and low-fertility or saline soils. Camelina 

also has lower water, pesticides and fertilizer requirements than traditional commodity oilseed crops (e.g., 

apeseed/canola, soybean and sunflower). Moreover, 

camelina is well adapted to the more northerly regions 

of North America, Europe and Asia. As such, it may 

serve in a rotational cycle in the Northern Hemisphere 

where winter wheat (Triticum spp.) is typically planted, 

thus facilitating disruption of undesirable weed and 

pest cycles [92,93]. The yield of camelina at maturity 

is 1500–3000 kg seeds/ha. The lipid content of individual seeds ranges between 36 and 47 wt% [65]. The 

resulting yield of camelina oil is thus calculated to be 

540–1410 kg/ha, which, as seen in Table 6, surpasses the 

yield of soybean oil and is approximately equal to that 

of rapeseed oil. a-linolenic acid comprises 32–40 wt% 

of the FA composition of camelina oil (Table 7). Other 

FAs in quantities above 10 wt% include linoleic, oleic 

and 11-eicosenoic acids [12,65,92–95]. 

Extraction of oil from camelina seeds by mechanical 

expeller yields a seed meal that consists of approximately 

10% residual oil, 45% crude protein, 13% fibers, 5% 

minerals and other minor constituents such as glucosinolates and vitamins [92]. The concentration of glucosinolates in dry camelina seeds ranges from 13 to 

36 μmol/g with a mean concentration of 24 μmol/g [96]. 

Consequently, camelina meal cannot exceed 10 wt% of the total food 

ration given to feedlot cattle and 

chickens in the USA. However, a 

ceiling of 10% represents significant 

market potential where a large number of livestock animals is located, 

thus representing an important 

revenue stream for camelina meal. 

The FFA content of crude camelina oil is sufficiently low to allow 

for direct conversion to FAMEs, 

thereby eliminating the need for acid pretreatment. 

However, a higher yield of FAMEs was reported when 

pretreatment was performed [12,95]. Camelina oil was 

successfully converted into biodiesel by the classic 

homogeneous base-catalyzed method, as well as with 

heterogeneous metal oxide catalysts, both with and 

without microwave irradiation and at noncatalytic suband super-critical conditions employing co-solvents with 

methanol [12,95,97–100]. The fuel properties (Table 8) of 

camelina-based biodiesel are similar to those of biodiesel 

prepared from soybean oil, thus indicating its acceptability for use as biodiesel [12,95]. It should be noted, 

based on the relatively high content of polyunsaturated 

FAMEs contained in camelina oil-derived biodiesel, 

that antioxidant additives would be needed to meet the 

oxidative stability specifications contained in ASTM 

D6751 and EN 14214. However, both ASTM D6751 

and EN 14214 recommend that antioxidants be added 

to all biodiesel fuels immediately after their production, regardless of the feedstock from which they were 

prepared. Additionally, FAEEs prepared from camelina 

oil along with FAMEs were evaluated as blend components in petrodiesel (<15 ppm S). Camelina-based 

petrodiesel blends exhibited fuel properties comparable 

to the analogous soybean-based blends [12]. 

Field pennycress

Field pennycress is a winter annual belonging to the 

Brassicaceae family that is also known as stinkweed or 

French weed. Native to Eurasia but with an extensive 

distribution throughout the world, field pennycress is 

Table 6. Yield of plant oil from several feedstocks.

Common name Latin binomial Oil content/seed

(wt%)

Seed yield

(kg ha-1 year-1)

Oil yield

(kg ha-1 year-1)

Camelina Camelina sativa 36–47 1500–3000 540–1410

Field pennycress Thlaspi arvense 20–36 1120–2240 224–806

Jatropha Jatropha curcas 27–40 2000–5000 540–2000

Oil palm Elaeis guineensis 4000–10,000

Rapeseed Brassica napus 40–44 2680–3390 965–1342

Soybean Glycine max 18–22 2140–2840 347–562

Table 7. Distribution of principal fatty acids in several plant oils.

Fatty acid Camelina Field pennycress Canola Palm Soybean

C16:0 6.8 3.1 4.6 41.9 10.5

C18:0 2.7 0.5 2.1 4.6 4.1

C18:1 9c 18.6 11.1 64.3 41.2 22.5

C18:2 9c, 12c 19.6 22.4 20.2 10.3 53.6

C18:3 9c, 12c, 15c 32.6 11.8 7.6 0.1 7.7

C20:1 11c 12.4 8.6 Trace None Trace 

C22:1 13c 2.3 32.8 None None None

Others 5.0 9.7 1.2 1.9 1.6
204 Biofuels (2012) 3(2) future science group

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highly adapted to a wide variety of climatic conditions 

[48,90,91,101–103]. Normally considered to be an agricultural pest (weed) by farmers, field pennycress readily 

grows from fall to spring with none or minimal agricultural inputs (fertilizer, pesticides and water). Because 

of its growth habit, it can be successfully planted and 

harvested without disrupting annual soybean production, thus not displacing existing agricultural production. In addition, field pennycress is tolerant of lands 

not otherwise suited for agricultural production, does 

not compete with the food chain, is compatible with 

existing farm infrastructure and practices, and has 

high seed oil content (20–36 wt%) [48,90,91,101,102]. 

The typical yield from wild populations is 1420 kg 

seed/ha, although 1120–2240 kg/ha is the expected 

range due to variability in various climatic and soil 

conditions along with inputs and other factors [48,90]. 

The resulting yield of field pennycress oil is thus calculated to be 224–806 kg/ha, which, as seen in Table 6, 

surpasses the yield of soybean oil but is lower than that 

for rapeseed oil. Erucic acid is the principal component 

of field pennycress oil (Table 7). The remaining FA distribution consists mostly of oleic, linoleic and linolenic 

acids [48,90,102]. Current agronomic efforts are focused 

on increasing oil yield, lowering erucic acid content 

and reducing the growing season to enable rotation 

with corn [90].

The concentration of glucosinolates in pennycress 

seed and its seed meal is sufficient to serve as a volatile 

biofumigant [91]. Both hexane-extracted and mechanically expelled field pennycress seed meals release allylisothiocyanate (AITC) when placed in contact with water. 

Myosinase is the enzyme responsible for decomposition 

of glucosinolates into AITC, which is the aglycone of 

sinigrin (the principal glucosinolate in field pennycress). 

Interestingly, sinigrin is nontoxic but its degradation 

product, AITC, is toxic to both plants and animals. 

Field pennycress seed meal is effective at inhibiting the 

germination and growth of weed seeds in laboratory test 

experiments, as well as in test plots, due to the growthinhibitory activity of AITC. When incorporated at 1.0 

wt% into soil, seed meal containing AITC completely 

inhibited the appearance of weeds. This practice may 

prove useful to organic farmers who wish to use green 

practices for weed control within field plots [91]. As a 

result of its high glucosinolate content, AITC-containing 

seed meal cannot be directly used as a component in 

feed for livestock animals. However, if the myrosinase 

enzyme responsible for biological conversion of sinigrin 

to AITC is deactivated, then field pennycress seed meal 

is suitable as an animal feed, as it would be free of AITC. 

Deactivation of myrosinase is performed by passing field 

pennycress seeds through a commonly available seed 

conditioner. The seed conditioner denatures myrosinase 

by subjecting the seeds to elevated temperature (85°C) 

for an extended period of time (24 h). An additional 

advantage of seed-conditioned field pennycress seeds 

is that a higher yield of oil is obtained when passed 

through a mechanical expeller relative to unconditioned 

seeds, due to extraction efficiency increases related to the 

increased surface area of conditioned seeds. In summary, 

seed-conditioned field pennycress seed meal is suitable as 

an animal feed supplement because it does not contain 

AITC [87,91,101,104–106]. 

The content of FFAs in crude field pennycress oil is 

sufficiently low to allow for direct conversion to FAMEs 

following the classic homogenous, alkaline-catalyzed 

methodology, thereby eliminating the need for acid 

pretreatment. However, a higher yield of FAMEs was 

reported when pretreatment was performed [48]. The 

cold-flow properties (Table 8) of field pennycress-based 

biodiesel indicate significantly improved low-temperature fluidity relative to camelina and commodity 

oil-derived FAMEs. Such a result has important implications for use of biodiesel during winter months in temperate climates where ambient temperatures regularly 

reach 0°C or lower [48]. However, the high content of 

methyl erucate (C22:1 13c) in field pennycress-derived 

biodiesel results in a higher KV (5.24 mm2/s at 40°C) 

than that typically reported for commodity-derived 

FAMEs (4.10–4.50 mm2/s at 40°C). The value obtained 

for field pennycress-derived biodiesel (5.24 mm2/s) is not 

within the range specified in EN 14214 (3.5–5.0 mm2/s) 

but is within the ASTM D6751 limit (1.9–6.0 mm2/s). 

Methods to lower KV include reduction of methyl erucate content through genetic modification, breeding 

techniques or simply through blending with less-viscous 

FAMEs [107].

Table 8. Selected fuel properties of biodiesel prepared from camelina and field pennycress oils, compared 

with soybean-, canola- and palm oil-based biodiesel fuels.

Camelina Field pennycress Canola Palm Soybean

Cloud point (°C) 3 -10 0 17 0

Pour point (°C) -4 -18 -9 15 -3

Cold filter plugging point (°C) -3 -17 -7 12 -4

Induction period, 110°C (h) 2.5 4.4 6.4 10.3 5.0

Kinematic viscosity, 0°C (mm2

/s) 4.15 5.24 4.42 4.58 4.12
Biodiesel from alternative oilseed feedstocks Review

future science group www.future-science.com 205

Executive summary

Biodiesel fuel standards

 The American biodiesel standard is American Society for Testing and Materials D6751 and the European biodiesel standard is EN 14214.

Advantages & disadvantages of biodiesel 

 Advantages: domestic and renewable, inherent lubricity, low toxicity, high flash point, superior biodegradability, negligible sulfur and 

aromatics content, lower overall exhaust emissions and positive energy balance. 

 Disadvantages: oxidative and storage stability, low temperature operability, high feedstock cost, lower volumetric energy content and 

susceptibility to hydrolysis as well as microbial degradation.

Energy balance

 The net energy ratio (NER) for biodiesel prepared from soybean oil is 4.5:1.

 NER may vary depending on feedstock as well as with inputs and outputs selected for study.

Optimum reaction conditions

 A sixfold molar excess methanol is needed along with 0.5 wt% catalyst (with respect to triacylglycerols [TAGs]) to ensure that the 

transesterification reaction proceeds to completeness.

Influence of free fatty acids

 Free fatty acids (FFAs) react with homogeneous alkaline catalysts to form soap and water.

 FFAs irreversibly quench homogenous alkaline catalysts and reduce yield when present in concentrations above 2 wt%.

 FFAs promote dissolution of biodiesel into the glycerolic phase during purification, thus further depressing the final yield of biodiesel. 

Phase distribution during methanolysis

 Methanolysis commences as two immiscible phases as a result of the low solubility of TAGs in methanol. 

 Diacylglycerol and monoacylglycerol intermediates serve as emulsifiers to improve mass transfer.

 When near completion the reaction transforms into a second biphasic system consisting of ester- and glycerol-rich phases.

Chemical structure & common FAs

 Biodiesel consists of methanol esterified to FAs. 

 FAs are derived from TAGs of plant oils and animal fats, which consist of three FAs esterified to a glycerol backbone. 

 The five most common FAs in plant oils are palmitic, stearic, oleic, linoleic and linolenic acids. 

Influence of chemical structure on fuel properties

 Fuel properties are determined by the component fatty acid methyl esters that comprise biodiesel. 

 Monounsaturated fatty esters strike a balance between cold-flow properties, oxidative stability, kinematic viscosity and cetane number. 

Traditional feedstocks

 Up to 88% of the cost of biodiesel production is attributed to feedstock acquisition if refined commodity oils are utilized. 

 The most common feedstock in the USA is soybean oil. Canola and palm oils are most common in Europe and the tropics, respectively. 

Promising alternative feedstocks

 Desirable characteristics of alternative feedstocks include adaptability to temperate climates, high oil content, favorable FA composition, 

compatibility with existing farm practices, low agricultural inputs, definable growth season, uniform seed maturation rates, potential 

markets for byproducts, adaptability to fallow lands, not competing with the food chain and not displacing existing agricultural production. 

 Members of the Brassicaceae family are of particular interest because the above criteria are met. Historically, Brassicas have been used as 

cover crops to prevent soil erosion and for weed management. Rapeseed is a commercially significant example from this family. 

Camelina

 The yield of camelina oil is 540–1410 kg/ha, which surpasses soybean oil and is approximately equal to rapeseed.

 Camelina seed meal contains 13–36 μmol/g of glucosinolates, which is sufficient to restrict its use as a livestock feed supplement to no 

more than 10 wt%.

 The primary FA in camelina oil is linolenic acid, with linoleic, oleic and 11-eicosenoic acid also present in significant quantities. 

 The fuel properties of camelina-based biodiesel are similar to those of biodiesel prepared from soybean oil, thus implicitly indicating its 

acceptability for use as biodiesel. 

 Antioxidant additives would be needed to meet the oxidative stability specifications listed in American Society for Testing and Materials 

D6751 and EN 14214. 

Field pennycress

 The yield of field pennycress oil is 224–806 kg/ha, which surpasses the yield of soybean oil but is lower than that reported for rapeseed oil.

 Field pennycress seed meal may be used as a livestock feed supplement if myrosinase is first denatured prior to lipid extraction. 

 Erucic acid is the principal component. Other FAs in quantities above 10 wt% include oleic, linoleic and linolenic acids.

 The cold-flow properties of field pennycress biodiesel indicate significantly improved low-temperature fluidity relative to camelina and 

commodity oil-derived fatty acid methyl esters.

Conclusion

 Problems remaining to be solved include relatively poor cold-flow properties, poor oxidative and storage stability, and high feedstock cost. 

 Development of alternative feedstocks with favorable agronomic traits that do not compete with food production and do not have 

food-related applications show great promise to enhance biodiesel production while simultaneously improving process economics. 
206 Biofuels (2012) 3(2) future science group

 Review Moser

Conclusion

Biodiesel exhibits several important technical advantages over petrodiesel, but resolution of technical issues 

would greatly facilitate its market acceptance and penetration. Outstanding technical deficiencies of biodiesel 

relative to petrodiesel include cold-flow properties as 

well as oxidative and storage stability. From an economic standpoint, deployment of low-cost alternative 

feedstocks would significantly improve biodiesel process 

economics.

Commodity oilseed crops are relatively expensive, in 

many cases do not have optimum FA compositions, have 

competing food-related applications and, in some cases, 

the lipids are not obtained in high yields from seeds. 

Development of alternative feedstocks with favorable 

agronomic traits that do not compete with food production and do not have food-related applications have great 

promise, especially if they have high oil density (kg/ha) 

and can be grown in close proximity to human population centers. Two such examples are camelina and field 

pennycress, which both belong to the Brassicaceae 

family and can overwinter on otherwise fallow farmland with minimal agricultural inputs. The resulting 

biodiesel fuels from these alternative feedstocks compare favorably with esters produced from traditional 

commodity fats and plant oils.

Future perspective

From a policy standpoint, it is anticipated that the next 

5–10 years will see an increase in the number of biodiesel usage mandates at both the B5 and B20 levels and 

that governments (both local and national) will increase 

already existing mandates. Such actions will accelerate the acceptance and adoption of biodiesel while 

simultaneously stimulating rural economies around 

the world. It is anticipated that the primary market 

for biodiesel in the near- to long-term future is as a 

blend component in petrodiesel, although secondary 

markets for B100 may lie in niche applications such as 

farm equipment, marine or underground applications, 

as well as in environmentally sensitive areas such as 

national parks. From a technical aspect, new developments in separation methods (such as membranes 

and ion-exchange resins) will facilitate purification of 

biodiesel while also increasing final product quality. 

Improved purification methods, such as membranes 

and resins, may also reduce the amount of wastewater 

generated during biodiesel production, thus representing an important environmental advancement. Further 

breakthroughs may include implementation of new and 

existing heterogeneous catalyst technologies in an effort 

to economically convert feedstocks high in FFA content 

into high-quality biodiesel in high yield, thereby avoiding the classic two-step esterification/transesterification 

protocol commonly utilized today. Lastly, discovery 

and further development of existing alternatives to 

commodity lipids will enhance feedstock availability 

while simultaneously reducing feedstock cost for production of biodiesel, both of which will combine to 

result in increased global biodiesel production for the 

foreseeable future. 

Disclaimer

Mention of trade names or commercial products in this publication 

is solely for the purpose of providing specific information and does 

not imply recommendation or endorsement by the US Department 

of Agriculture. The US Department of Agriculture is an equal 

opportunity provider and employer.

Financial & competing interests disclosure

The author has no relevant affiliations or financial involvement with 

any organization or entity with a financial interest in or financial 

conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock 

ownership or options, expert testimony, grants or patents received or 

pending, or royalties.

No writing assistance was utilized in the production of this 

manuscript. 

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